Intelligent discharge control for modular multilevel converter
AssigneeVestas Wind Systems A/S
InventorsCem Özgür Gerçek, Lars Helle, Ciprian Biris
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Abstract
This disclosure proposes procedures and systems for discharging system capacitors and de-energizing power transmission systems having Modular Multilevel Converter (MMC) topologies by intelligent control of MMC cell components including configuration of bypass and insert switches using integrated DC choppers to effectively de-energize MMC cell capacitors and/or DC-link capacitors under operating conditions such as after a normal stop, for protection against over-voltages, dumping turbine energy, and under certain hardware fault conditions.
Claims20
A method of controlling a wind turbine modular multilevel converter (MMC) system comprising a plurality of MMC cells connected in series, each of the plurality of MMC cells comprising at least two main switches and an integrated direct current (DC) chopper, the method comprising:
- detecting a system discharge event;
- and
- controlling the integrated DC choppers to de-energize one or more MMC cell capacitors in each of the plurality of MMC cells in response to the system discharge event.
A method of de-energizing a wind turbine MMC system, the MMC system comprising a plurality of series-connected MMC cells, and a DC-link having a first DC-link voltage rail and a second DC-link voltage rail, the method comprising:
- enabling a first discharge path from the first DC-link voltage rail, through the plurality of series-connected MMC cells, to the second DC-link voltage rail;
- and
- grounding the second DC-link voltage rail with an earthing resistor;
- wherein the first discharge path includes the earthing resistor.
A method of de-energizing a wind turbine MMC system, the MMC system comprising a plurality of series-connected MMC cells, and a DC-link having a first DC-link voltage rail and a second DC-link voltage rail, the method comprising:
- enabling a first discharge loop having a current path from the first DC-link voltage rail, through the plurality of series-connected MMC cells, to the second DC-link voltage rail;
- and
- enabling a second discharge loop that includes a current path from the first DC-link voltage rail, through a second plurality of series-connected MMC cells, to the second DC-link voltage rail;
- wherein the first discharge loop includes MMC cells from a different phase.
Dependencies are inferred from the claim text.